The present invention is related to thermoplastic elastomeric compositions particularly useful for tire and other industrial rubber applications, reinforced or otherwise, that require impermeability characteristics.
EP 0 722 850 B1 discloses a low-permeability thermoplastic elastomeric composition that is excellent as an innerliner in pneumatic tires. This composition comprises a low permeability thermoplastic in which is dispersed a low permeability rubber. EP 0 969 039 A1 discloses a similar composition and teaches that the small particle size rubber dispersed in the thermoplastic was important to achieve acceptable durability of the resulting composition.
There are also examples of the use of a thermoplastic elastomer composed of a rubber and a thermoplastic for use as an innerliner in a tire. But, in general, a flexible material of the type disclosed therein has low heat resistance. When the thermoplastic material in the composition has a melting point less than the tire vulcanization temperature, when the tire curing bladder is released at the end of the curing cycle, the inside surface of the tire may have defects due to the thermoplastic material of the composition sticking to rubber of the curing bladder.
Controlling the viscosity difference between the two different materials in the composition is also considered important, as the viscosity difference affects the dispersed rubber particle size. To obtain the desired viscosity reduction, it is known to add a plasticizer to the composition. The most common plasticizer used is butylbenzylsulfonamide (BBSA). However, when using BBSA as the plasticizer, the BBSA is not bound or grafted to the thermoplastic resin in the composition and the unbound BBSA is known to volatize out during subsequent heating and downstream processing of the thermoplastic elastomer. Such volatilization of the BBSA can result in undesirable blemishes on the product surface, this is also known as ‘blooming’ and while not detrimental to the performance of the product, does result in an unsatisfactory appearance and an impression of a faulty product. Additionally, it is desired to reduce the amount of volatiles that are released into the atmosphere during downstream operations using the thermoplastic elastomer.
To that end, the inventors have previously sought to reduce the amount of BBSA used as a plasticizer in the thermoplastic elastomer compositions. The resulting compositions had lower BBSA volatile organic compounds and surprisingly good fluidity. The melting point of the new compositions was also higher, which is a desirable attribute. No penalties in engineering properties were incurred. However, attempts to fully eliminate the BBSA from the elastomer-rich compositions, until the present invention, were unsuccessful as the elastomer component of the composition failed to achieve the desired phase inversion and did not convert to a dispersed phase in a thermoplastic resin domain and the resulting composition was too soft. To achieve the desired phase inversion, a small level of BBSA, approximately 2.5 wt % based on the total weight of the composition, had to be present in the composition during composition mixing. The present invention is directed to addressing the desire to continue to reduce, and preferably eliminate BBSA, and in particular unbound sulfonamides, in the composition.